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Re: [PATCH v12 3/7] [RISCV_PM] Support CSRs required for RISC-V PM exten

From: Richard Henderson
Subject: Re: [PATCH v12 3/7] [RISCV_PM] Support CSRs required for RISC-V PM extension except for the h-mode
Date: Wed, 29 Sep 2021 06:55:55 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

On 9/28/21 3:00 PM, Alexey Baturo wrote:
+    switch (env->priv) {
+    case PRV_M:
+        cur_bit_pos = M_PM_CURRENT;
+        break;
+    case PRV_S:
+        cur_bit_pos = S_PM_CURRENT;
+        break;
+    case PRV_U:
+        cur_bit_pos = U_PM_CURRENT;
+        break;
+    default:
+        g_assert_not_reached();
+    }
+    pm_current = get_field(env->mmte, cur_bit_pos);

Nit: If you have a look at what the get_field macro does, you'll see that you always want to give it a constant, so the compiler can fold all of the arithmetic into a constant bitfield extract. It is not a win to pull the field argument out into a variable like this.

For this reason I prefer the hw/registerfields.h interface -- it is more 
difficult to misuse.


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